The present invention relates to oxadiazole compounds containing 4,6-bis-trichloromethyl-s-triazin-2-yl groups, to a process for their preparation and to a photosensitive composition containing these compounds.
It is known to employ aromatic or heterocyclic compounds containing trichloromethyl groups as initiators for various photochemical reactions.
DE-A 22 43 621 discloses s-triazines substituted by one or two trichloromethyl groups and one chromophoric group that are suitable as photoinitiators in photopolymerizable compositions and as acid donors in a mixture with acetals that can be split by acid. These compounds include those that absorb light in the visible region of the electromagnetic spectrum and act as photoinitiators.
Similar compounds, in which an at least binuclear aromatic radical as a chromophoric group is bonded directly to the triazine ring, are disclosed in DE-A 27 18 259 (U.S. Pat. No. 4,189,323).
EP-A 137 452 describes similar 4,6-bis-tri-chloromethyl-s-triazines having an optionally-substituted styryl group in the 2-position. The absorption peaks of these compounds are mostly in the near ultraviolet region.
DE-A 28 51 472 describes photosensitive compositions containing 2-halogenomethyl-5-vinyl-1,3,4-oxadiazole derivatives as photoinitiators.
Similar compounds that act as photoinitiators are disclosed in DE-A 35 06 274. These compounds have absorption peaks at longer wavelengths.
DE-A 30 21 590 and DE-A 30 21 599 disclose halogenoxazoles substituted by trichloromethylphenyl groups that are suitable as photoinitiators, like the above-mentioned compounds.
Moreover, EP-A 135 348 and EP-A 135 863 disclose 1-alkyl-2-carbonylmethylene-benzothiazoles and similar heterocyclic compounds, carrying a trichloromethylphenyl group on the carbonyl group. These compounds also have a maximum sensitivity in the near ultraviolet region.
The reaction conditions for preparing many of these compounds are fairly drastic resulting in a yield that is relatively low and the formation of undesired by-products that are difficult to separate (for example, DE-A 22 43 621, DE-A 27 18 259 or 28 51 472). With many known initiators, the inadequate sensitivity makes it necessary to combine different initiator systems. It has, moreover, been found that precisely the most sensitive of the known initiators do not have a storage stability which meets the requirements of practical application in photosensitive compositions, in particular in contact with copper surfaces. Most of the known photoinitiators that can also be used as photolytically-activatable acid donors, furthermore, have maximum sensitivities between 380 and 420 nm.
In modern exposure technology, however, two new trends appear, that have opposite directions. On the one hand, for the generation of finer structures and an improved reproduction thereof, in particular in microelectronics, light sources having maximum emissions at shorter wavelengths, e.g., at 365 nm, will be employed to an increasing extent in the future. In the graphic industry, on the other hand, light sources, e.g., lasers, are used in the course of digitization of information, that emit light in the visible region of the electromagnetic spectrum, in general above 450 nm.